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918

Appendix IIL

connected to E E by the coupling rods H H. The bars to be
welded are first placed cold in the vices, and the screws A A
are adjusted to suit the thickness of the work, so that the final
grip may be given by the eccentric jaws B B. The welding heat
is next obtained, and, while two men put the pieces quickly in
the vice jaws with the hot surfaces in contact at r>, a third man
pulls over the lever F, and thus squeezes the joint to a perfect
weld which may be finished with hammer in the usual way. The
leverage is about 200 to i, and a pressure of about 20 tons is
produced at j. The machine may be further applied to jumping
or upsetting, and a reversal of pull will elongate or draw out
a bar

CHAPTER V.

Pp. 138 6° 169. Loss on Return Stroke.-u~.lt is shewn in
this chapter that the return stroke in reciprocating machine tools,
when no useful work is done, generally takes place at a higher
speed. The introduction of electric motors for individual driving
has enabled us to measure the work absorbed on both advance
and return strokes, and has shewn that in planing machines the
total work used on each stroke is almost identical, though that of
the return stroke is slightly less. This means that the work at
the tool point is but a small part of the total 'work of driving
and cutting. Further, if the return stroke be done in one nth
of the time of the advance, the horse-power on the return is
about n times that of the advance stroke, which, of course, follows
from the previous statements. It is evident, therefore, that the
quick return stroke does not save in work done per stroke, but is
a saving in time, while absorbing a higher horse-power, pro-
portional to speed.

CHAPTER VII.

P. 831. Appendix II.:—Automatic Feed-Water Regu-
lator.—This apparatus is an important adjunct to any water-tube
boiler, for where little water is contained the level fluctuates con-
siderably with variable engine-power. The well-known Belleville